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| Motion control, S-curves and other stuff >> controlling lift with DC motor |
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| capt bullshot:
--- Quote --- I have to investigate what is the real source of that problem. --- End quote --- Good luck, I'm quite confident you're able to find the root cause. Need 50kHz or not: No idea, except higher switching frequency allows for lower inductance. That particular motor indeed is pretty low inductance, so 20kHz to 100kHz looks appropriate for a rated 100uH / real 30uH. Not a big deal for modern MOSFETs. Running the timer @ 144MHz: should work if the datasheet says so ;) |
| krisRaba:
Ok, problem solved and actually it was something stupid ;-) I forgot that value written to BDTR (DTG) register to set deadtime is related to timer clock :palm: so after increasing clock frequency effective deadtime was decreased proportionally ;-) After increasing it as well power stage is cool as usually :-/O And signals from MCU looks ugly now.. but only with ground lead ;-) With spring ground connection on probe it is OK. But I will think about decreasing gate resistors a little bit. Now 10R is used so small bannana shape is visible on gate charging and discharging. Or maybe I will add diode+resistor in parallel just to turn it off faster and keep slower turn on time because of EMI... And what is most important current ripple significantly decreased with 50kHz PWM ;-) I wonder what will be the effect of additional chokes in serie, it should be even better ;-) |
| capt bullshot:
--- Quote from: krisRaba on October 24, 2019, 08:35:21 am ---Ok, problem solved and actually it was something stupid ;-) I forgot that value written to BDTR (DTG) register to set deadtime is related to timer clock :palm: so after increasing clock frequency effective deadtime was decreased proportionally ;-) After increasing it as well power stage is cool as usually :-/ --- End quote --- Business as usual ;) --- Quote ---And signals from MCU looks ugly now.. but only with ground lead ;-) With spring ground connection on probe it is OK. --- End quote --- Business as usual ;) --- Quote ---But I will think about decreasing gate resistors a little bit. Now 10R is used so small bannana shape is visible on gate charging and discharging. Or maybe I will add diode+resistor in parallel just to turn it off faster and keep slower turn on time because of EMI... --- End quote --- I've seen higher gate resistances working just fine - depends on the MOSFETs and it's just the usual power dissipation vs. EMI tradeoff game >:D --- Quote ---And what is most important current ripple significantly decreased with 50kHz PWM ;-) I wonder what will be the effect of additional chokes in serie, it should be even better ;-) --- End quote --- Business as usual :-+ |
| krisRaba:
--- Quote from: capt bullshot on October 24, 2019, 09:20:47 am --- --- Quote ---But I will think about decreasing gate resistors a little bit. Now 10R is used so small bannana shape is visible on gate charging and discharging. Or maybe I will add diode+resistor in parallel just to turn it off faster and keep slower turn on time because of EMI... --- End quote --- I've seen higher gate resistances working just fine - depends on the MOSFETs and it's just the usual power dissipation vs. EMI tradeoff game >:D --- End quote --- Yes, I know. I have seen even 100R in ST BLDC controller ;) Worked well with 6-step but it was a tragedy when I was trying to implement sinusoidal driving and had to be reduced ;) So it also depends on control scheme and your needs. But I am also aware that high rise times look good on DSO but are your enemy in EMI ;) But on other hand additional inductance should add some slope ;) I have just checked that driver already has 5R of internal resistance for LOW TO HIGH transition and 0.55R for HIGH TO LOW transition so it is already asymmetric. I will leave that for further testing in the future ;) --- Quote from: capt bullshot on October 24, 2019, 09:20:47 am --- --- Quote ---And what is most important current ripple significantly decreased with 50kHz PWM ;-) I wonder what will be the effect of additional chokes in serie, it should be even better ;-) --- End quote --- Business as usual :-+ --- End quote --- I have added 2x 4,7uH in series with motor windings and just as expected, current ripple has been decreased. It is not enormous change, something about 25%, but always something is better than nothing :-+ Does it mean that effective inductance of motor is about 37,6uH? I think so and it sounds quite realistic. It would be 36,5% of 103uH presented in datasheet and they were talking about 30-80% for calculations.. |
| capt bullshot:
--- Quote from: krisRaba on October 24, 2019, 10:00:24 am ---I have added 2x 4,7uH in series with motor windings and just as expected, current ripple has been decreased. It is not enormous change, something about 25%, but always something is better than nothing :-+ Does it mean that effective inductance of motor is about 37,6uH? I think so and it sounds quite realistic. It would be 36,5% of 103uH presented in datasheet and they were talking about 30-80% for calculations.. --- End quote --- Yes, I'd agree using the same rough (and probably incorrect) calculation pointing to the ballpark range. Good enough for a plausible estimate. |
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